Coatings and paints are routinely used to beautify and protect substrates. The most simple coatings and paints are made of a polymer (the binder) in a solvent (the vehicle), which is commonly called a lacquer. Paints and coatings modify the appearance of an object by adding color, gloss, or texture, and by blending with or differentiating from a surrounding environment. For example, a surface that is highly light scattering can be made glossy by the application of a paint that has a high gloss. Conversely, a glossy surface can be made to appear flat. Thus, the painted surface is hidden, altered, and ultimately changed in some manner by the presence of the coating. In addition, paints also protect the surface from the surrounding elements and prevent or reduce the corrosive process.
Paints and coatings, while protecting the substrate from external environment, can themselves get dirty over time. The dirt can dull the coating by increasing light scattering or by modifying the color of the coating. Dirt can also affect the durability of a paint. A surface with a hydrophilic coating, however, would allow water to spread out in a thin layer, sweeping dirt off the surface as the water thins out and trickles away. This type of “self-cleaning” behavior is advantageous to an exterior paint, as it keeps the coating clean without requiring extensive cleaning by the customer. A hydrophilic surface would allow water to sheathe over the surface and either solvate or even carry away the dirt molecules.
Biofouling represents a significant problem for any wetted surface or structure, and may result in interference with the normal use and condition of the surface or structure. Such interference can lead to premature break down of wetted structures and surfaces, and can have significant economic implications to a number of industries. Biofouling also results in decoloration of paint surfaces due to the compounds secreted by microorganisms and algae, and affect paint durability. Constant exposure of a surface or a structure to water results in the deposition of dissolved organic material as a thin film and recruitment of bacterial colonies, resulting in formation of a biofilm. Upon attaching to the surface, the bacteria release substances that further provide mechanical stability to the biofilm, through electrostatic forces such as hydrogen bonds and van der Walls interactions. As the attached bacterial cells begin to multiply, the biofilm thickens, further aiding attachment of larger organisms, such as plants, algae or animals. These larger organisms colonize the biofilm coated surfaces and secrete compounds, such as glycoproteins, which allows these organisms to become nearly permanently attached to a surface. Accordingly, there is a need to develop coatings with biocidal, hydrophilic and self-cleaning properties.